Laser processing device

ABSTRACT

A laser processing device including: a laser oscillator; a processing table; a transmission optical system for transmitting laser light emitted from the laser oscillator to the processing table; a processing head for condensing and radiating the laser light transmitted via the transmission optical system to an object to be processed; a moving mechanism for changing a relative position between the object to be processed and the laser light to be radiated to the object to be processed; and a variable curvature spherical mirror. The transmission optical system includes a reflective beam expander mechanism for collimating and magnifying the laser light from the laser oscillator. The reflective beam expander mechanism includes a spherical mirror and a concave mirror having different curvatures in two orthogonal axes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 14/401,572 filed Nov. 17, 2014,the entire contents of which is incorporated herein by reference. U.S.Ser. No. 14/401,572 is a National Stage of PCT/JP13/065214 filed May 31,2013, which was not published under PCT Article 21(2) in English andclaims the benefit of priority from Japanese Patent Application No.2012-135988 filed Jun. 15, 2012.

TECHNICAL FIELD

The present invention relates to a laser processing device forprocessing an object to be processed by condensing and radiating laserlight emitted from a laser oscillator to the object to be processed.

BACKGROUND ART

Hitherto, a laser processing device for processing an object to beprocessed by using laser light emitted from a laser oscillator has beenwell known (see, for example, Patent Literature 1).

FIG. 7 is a block diagram schematically illustrating an optical pathconfiguration of a related-art laser processing device described inPatent Literature 1.

In FIG. 7, laser light L generated from a laser oscillator 1 istransmitted to a processing lens (not shown) in a processing head 4 viaa transmission optical system to be condensed and radiated to an objectto be processed (not shown) placed on a processing table 2.

The processing table 2 and the processing head 4 include moving means 5capable of moving each of the processing table 2 and the processing head4 in at least one axial direction. The moving means 5 can move arelative position between the laser light L and the object to beprocessed in a desired direction and can locate the relative position ata desired position.

In this case, the moving means 5 is configured to move the processingtable 2 in an X axis direction and to move the processing head 4 in a Yaxis direction.

The transmission optical system for the laser light L includes areflective beam expander mechanism 106 that the laser light L from thelaser oscillator 1 enters, and a reflection mirror 8 for introducing thelaser light L emitted from the reflective beam expander mechanism 106into the processing head 4.

The reflective beam expander mechanism 106 includes a reflection mirror68 that the laser light L from the laser oscillator 1 enters, aspherical convex mirror 63 that the laser light L reflected by thereflection mirror 68 enters, and a spherical concave mirror 65 that thelaser light L reflected by the spherical convex mirror 63 enters.

The reflective beam expander mechanism 106 increases a beam diameter ofthe laser light L by a desired scaling factor irrespective of adivergence angle of the laser light L generated from the laseroscillator 1, and maintains an appropriate condensed light diameter at aprocessing point on the processing table 2.

It is known that, generally, astigmatism in accordance with an incidentangle occurs in light reflected by a spherical mirror such as thespherical convex mirror 63 or the spherical concave mirror 65. Inparticular, when astigmatism occurs in the laser light L in a laserprocessing device, the light condensation ability is reduced and thebeam shape becomes anisotropic at the processing point.

In this way, in a laser processing device of a type in which theprocessing head 4 moves, the reflective beam expander mechanism 106 formagnifying and collimating the laser light L is provided in the opticalpath in order to maintain an appropriate condensed light diameter at theprocessing point of the object to be processed. When a spherical mirroris used in the reflective beam expander mechanism 106, in order toinhibit astigmatism, it is necessary to restrict the incident angle withrespect to the spherical mirror to an acute angle.

Therefore, when a spherical mirror is used in the transmission opticalsystem of the laser processing device, in order to avoid lowering ofprocessing quality and occurrence of anisotropy in processing due toastigmatism, it is necessary to restrict the incident angle of the laserlight L with respect to the spherical mirror to an acute angle so thatthe astigmatism does not adversely affect the processing quality.

It is known that, generally, when the incident angle with respect to thespherical mirror is set to be an acute angle (desirably 15° or less),lowering of the processing quality due to astigmatism is negligible.

Therefore, in FIG. 7 (Patent Literature 1), the reflection mirror 68 inthe reflective beam expander mechanism 106 restricts incident angles ofthe laser light L with respect to the spherical mirrors (sphericalconvex mirror 63 and spherical concave mirror 65) to acute angles,respectively.

However, when the reflection mirror 68 for restricting the incidentangles with respect to the spherical mirrors is provided, the opticalpath is complicated, and further, in a strict sense, the astigmatismcannot be inhibited. Further, through absorption of the laser light byoptical elements in the complicated optical path, the thermal lenseffect is produced, and thus increase in the number of the opticalelements is a factor of processing instability.

CITATION LIST Patent Literature

[PTL 1] JP 05-305473 A

SUMMARY OF INVENTION Technical Problems

In the related-art laser processing device, when the reflective beamexpander mechanism including the spherical mirror is used as thetransmission optical system, the reflection mirror for restricting theincident angle with respect to the spherical mirror is provided as inPatent Literature 1, but there are problems in that the optical pathconfiguration is complicated and, in addition, that astigmatism cannotbe satisfactorily inhibited.

The present invention has been made in order to solve theabove-mentioned problems, and an object of the present invention is toobtain a laser processing device capable of satisfactorily restricting abeam divergence angle and radiating laser light without aberration andhaving a desired beam diameter to an object to be processed by using areflective beam expander mechanism whose optical path configuration isnot particularly complicated.

Solution to Problems

According to one embodiment of the present invention, there is provideda laser processing device, including: a laser oscillator for emittinglaser light; a processing table for placing an object to be processed; atransmission optical system for transmitting the laser light emittedfrom the laser oscillator to the processing table; a processing head forcondensing and radiating the laser light transmitted via thetransmission optical system to the object to be processed; and movingmeans for changing a relative position between the object to beprocessed and the laser light to be radiated to the object to beprocessed, in which the transmission optical system includes: areflective beam expander mechanism for collimating and magnifying thelaser light from the laser oscillator; and a variable curvaturespherical mirror, in which the reflective beam expander mechanismincludes a spherical mirror and a mirror having different curvatures intwo orthogonal axes, and in which the variable curvature sphericalmirror is placed between the spherical mirror and the mirror havingdifferent curvatures in two orthogonal axes.

Advantageous Effects of Invention

According to one embodiment of the present invention, in the reflectivebeam expander mechanism constructing the transmission optical system, byusing the mirror having different curvatures in two orthogonal axes, thebeam divergence angle can be satisfactorily restricted and the laserlight without aberration and having a desired beam diameter can beradiated to the object to be processed, without using the transmissionoptical system having a particularly complicated structure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram schematically illustrating an optical pathconfiguration of a laser processing device according to a firstembodiment of the present invention.

FIG. 2 is a block diagram schematically illustrating an optical pathconfiguration of a laser processing device according to a secondembodiment of the present invention.

FIG. 3 is a block diagram schematically illustrating an optical pathconfiguration of a laser processing device according to a thirdembodiment of the present invention.

FIG. 4 is a block diagram schematically illustrating a principal part ofa laser processing device according to a fourth embodiment of thepresent invention.

FIG. 5 is a block diagram schematically illustrating a principal part ofa laser processing device according to a fifth embodiment of the presentinvention.

FIG. 6 is a block diagram schematically illustrating a principal part ofa laser processing device according to a sixth embodiment of the presentinvention.

FIG. 7 is a block diagram schematically illustrating an optical pathconfiguration of a related-art laser processing device.

FIG. 8 is a structural view schematically illustrating a mirroradjusting mechanism according to a seventh embodiment of the presentinvention.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 1 is a block diagram schematically illustrating an optical pathconfiguration of a laser processing device according to a firstembodiment of the present invention.

In FIG. 1, the laser processing device according to the first embodimentof the present invention includes a laser oscillator 1 that emits laserlight L, a processing table 2 on which an object to be processed (notshown) is placed, a transmission optical system including a reflectivebeam expander mechanism 6 and a reflection mirror 8, and a processinghead 4 that radiates the laser light L that has passed through thetransmission optical system to the object to be processed.

The laser light L emitted from the laser oscillator 1 is collimated andmagnified by the reflective beam expander mechanism 6 provided in thetransmission optical system, and then is introduced into the processinghead 4 by the reflection mirror 8. After that, the laser light L iscondensed by a processing lens (not shown) in the processing head 4, andthen is radiated to the object to be processed on the processing table2.

Moving means 5 is provided to the processing table 2 and the processinghead 4. The moving means 5 horizontally moves the processing table 2 andthe processing head 4 in ranges from positions indicated by the solidlines to positions 2′ and 4′ indicated by the dotted lines,respectively.

The moving means 5 moves the processing table 2 in an X axis (dottedarrow) direction and moves the processing head 4 in a Y axis (dottedarrow) direction under the control of control means (not shown), therebychanging a relative position between the laser light L and the object tobe processed to enable processing at a desired position to be processed.

Note that, in FIG. 1, in order to adjust the relative position betweenthe laser light L and the object to be processed, the moving means 5 forchanging the relative position between the processing table 2 and theprocessing head 4 is used, but moving means for driving only theprocessing head 4 may also be used.

The reflective beam expander mechanism 6 includes at least one mirrorhaving different curvatures in two orthogonal axes.

In FIG. 1, the reflective beam expander mechanism 6 includes a sphericalconvex mirror 63 that reflects the laser light L from the laseroscillator 1 and a concave mirror 62 having different curvatures in twoorthogonal axes.

The two orthogonal axes of the concave mirror 62 have curvaturesdifferent from each other, and the concave mirror 62 further reflectsthe laser light L reflected by the spherical convex mirror 63 to causethe laser light L to enter the reflection mirror 8 on the processingtable 2 side.

Note that, in this case, the concave mirror 62 having differentcurvatures in two orthogonal axes and the spherical convex mirror 63 areused in the reflective beam expander mechanism 6, but a convex mirrorhaving different curvatures in two orthogonal axes and a sphericalconcave mirror may also be used.

Further, the arrangement order of the concave mirror 62 and thespherical convex mirror 63 is not limited to that in the configurationillustrated in FIG. 1, and the arrangement order of the mirrors may beset in reverse order.

As the simplest reflective beam expander mechanism that collimates andincreases the beam diameter of the laser light L, it is conceivable touse a spherical convex mirror and a spherical concave mirror, but, asdescribed above, astigmatism in accordance with an incident angle occursin light reflected by a spherical mirror, and processing quality issignificantly lowered due to the anisotropic beam shape and degradedlight condensation ability caused by the astigmatism.

On the other hand, in the first embodiment of the present invention, theconcave mirror 62 having different curvatures in two orthogonal axes isused in the reflective beam expander mechanism 6, and the curvatures ofthe two axes of the concave mirror 62 are designed so that aberration isnot caused in the reflected light.

As a result, no restriction is imposed on the incident angle of thelaser light L, and thus an optical path design that uses the concavemirror 62 as a reflection mirror is possible. Thus, the beam diametercan be magnified and collimated not only without restricting theincident angle on the spherical convex mirror 63 but also withoutcausing astigmatism.

As described above, the laser processing device according to the firstembodiment (FIG. 1) of the present invention includes the laseroscillator 1 for emitting the laser light L, the processing table 2 onwhich the object to be processed is placed, the transmission opticalsystem for transmitting the laser light L emitted from the laseroscillator 1 to the processing table 2, the processing head 4 forcondensing and radiating the laser light L transmitted via thetransmission optical system to the object to be processed, and themoving means 5 for changing the relative position between the object tobe processed and the laser light L to be radiated to the object to beprocessed.

The transmission optical system includes the reflective beam expandermechanism 6 for collimating and magnifying the laser light L from thelaser oscillator 1, and the reflective beam expander mechanism 6includes a mirror having different curvatures in two orthogonal axes.

The reflective beam expander mechanism 6 includes the spherical convexmirror 63 and the concave mirror 62 having different curvatures in twoorthogonal axes. Alternatively, the reflective beam expander mechanism 6includes a spherical concave mirror and a convex mirror having differentcurvatures in two orthogonal axes.

By using a mirror designed so that two orthogonal axes thereof havecurvatures different from each other so as to inhibit aberration whenreflecting light in the reflective beam expander mechanism 6 formagnifying and collimating the laser light L in this way, a beamdivergence angle can be satisfactorily restricted and the laser light Lwithout aberration and having a desired beam diameter can be radiated toan object to be processed by using the reflective beam expandermechanism 6 whose optical path configuration is not particularlycomplicated.

Further, no restriction is imposed on the incident angle of the laserlight L with respect to the mirror having different curvatures in twoorthogonal axes, and thus the optical path design flexibility isenhanced and the optical system is simplified.

Further, the reflection mirror 68 for restricting the incident anglewith respect to a spherical mirror as in the related-art device (FIG. 7)can be eliminated and the number of optical elements in the transmissionoptical system can be reduced to simplify the optical structure. Thus,influence of the thermal lens effect of the optical elements is reduced,which enables stable processing over a long period of time.

Note that, in FIG. 1, in order to inhibit aberration during reflection,the incident angle of the laser light L with respect to the sphericalconvex mirror 63 is restricted to an acute angle. However, when thecurvatures of the concave mirror 62 are designed so that astigmatismthat occurs when the concave mirror 62 gives reflection and astigmatismof reflected light that occurs in accordance with the incident anglewith respect to the spherical mirror 63 are canceled out, the incidentangle of the laser light L with respect to the spherical convex mirror63 is not restricted to an acute angle.

Second Embodiment

Note that, in the above-mentioned first embodiment (FIG. 1), thereflective beam expander mechanism 6 including the concave mirror 62having different curvatures in two orthogonal axes and the sphericalconvex mirror 63 is used, but, as illustrated in FIG. 2, a reflectivebeam expander mechanism 6A including a convex mirror 61 having differentcurvatures in two orthogonal axes and the concave mirror 62 havingdifferent curvatures in two orthogonal axes may also be used.

FIG. 2 is a block diagram schematically illustrating an optical pathconfiguration of a laser processing device according to a secondembodiment of the present invention. The same components as thosedescribed above (see FIG. 1) are denoted by the same reference symbolsas those described above, and detailed description thereof is omittedherein.

In FIG. 2, the reflective beam expander mechanism 6A includes the convexmirror 61 having different curvatures in two orthogonal axes and theconcave mirror 62 having different curvatures in two orthogonal axes.

In the reflective beam expander mechanism 6 described above (FIG. 1),only one mirror having different curvatures in two orthogonal axes isused, but, in the reflective beam expander mechanism 6A according to thesecond embodiment (FIG. 2) of the present invention, two mirrors eachhaving different curvatures in two orthogonal axes (convex mirror 61 andconcave mirror 62) are used.

By using two mirrors each having different curvatures in two orthogonalaxes in the reflective beam expander mechanism 6A in this way, norestriction is imposed on the incident angles of the laser light L withrespect to the mirrors in the reflective beam expander mechanism 6A.Thus, the optical path design flexibility is enhanced and the reflectionmirror 68 for restricting the incident angle becomes unnecessary, whichreduces the influence of the thermal lens effect to stabilize theprocessing precision.

Further, all the mirrors in the transmission optical system can be usedas reflection mirrors, and thus the reflection mirror 8 on theprocessing table 2 side becomes unnecessary. Thus, the transmissionoptical system can be further simplified.

Further, the influence of the thermal lens effect of the opticalelements is further reduced, which enables stable processing over a longperiod of time.

Third Embodiment

Note that, in the above-mentioned first and second embodiments (FIG. 1and FIG. 2), the processing table 2 movable in the X axis direction isused, but an immovable processing table 2A may also be used asillustrated in FIG. 3.

FIG. 3 is a block diagram schematically illustrating an optical pathconfiguration of a laser processing device according to a thirdembodiment of the present invention. The same components as thosedescribed above (see FIG. 1 and FIG. 2) are denoted by the samereference symbols as those described above, and detailed descriptionthereof is omitted herein.

In FIG. 3, moving means 5A is provided to the processing head 4 on theprocessing table 2A, for moving the processing head 4 in the X axisdirection and in the Y axis direction in ranges from the positionindicated by the solid lines to positions 4′ indicated by the dottedlines.

Further, in the transmission optical system for the laser light L, anoptical path length fixing mechanism 7 is inserted between thereflective beam expander mechanism 6A and the reflection mirror 8 on theprocessing table 2A side.

In this case, the processing table 2A is larger than the processingtable 2 described above and has a processing region larger than that ofthe processing table 2. It is not efficient to drive the processingtable 2A, and hence the moving means 5A changes the relative positionbetween the laser light L and an object to be processed only by drivingthe processing head 4.

Note that, when the processing head 4 is moved in the Y axis direction,a reflection mirror 28 is also moved in a range from a positionindicated by the solid lines to a position 28′ indicated by the dottedlines.

Further, under this state, an optical path length of the laser light Lfrom the laser oscillator 1 to the processing head 4 greatly differsdepending on a processing position on the processing table 2A, which maycause an error in the condensed light diameter of a beam radiated to anobject to be processed. Therefore, the optical path length fixingmechanism 7 for cancelling out fluctuations in optical path length tomake compensation is provided.

The optical path length fixing mechanism 7 includes a mirror group 78including a plurality of mirrors for causing a direction of travel ofincident light and a direction of travel of output light to be oppositeand in parallel to each other.

Further, the optical path length fixing mechanism 7 includes a movingmechanism 79 for translating the mirror group 78 in a range from aposition indicated by the solid lines to a position 78′ indicated by thedotted lines.

The moving mechanism 79 adjusts, under the control of control means (notshown), the optical path length of the laser light L to be always at apredetermined value by moving the position of the mirror group 78 so asto cancel out change in optical path length caused by the movement ofthe processing head 4.

Note that, in FIG. 3, the optical path length fixing mechanism 7 is usedwith respect to the processing table 2A that changes the relativeposition between the laser light L and an object to be processed only bymoving the processing head 4, but the optical path length fixingmechanism 7 can also be applied to a configuration in which both theprocessing head 4 and the processing table 2 are moved as describedabove (FIG. 1 and FIG. 2).

Further, a case where the reflective beam expander mechanism 6Aaccording to the above-mentioned second embodiment (FIG. 2) is used isdescribed, but this embodiment is similarly applicable to a case wherethe reflective beam expander mechanism 6 according to theabove-mentioned first embodiment (FIG. 1) is used.

The laser light L emitted from the reflective beam expander mechanism 6Ais collimated, and thus the condensed light diameter of the laser lightL radiated to an object to be processed on the processing table 2Aideally does not change even when the optical path length changes.However, in a strict sense, it is impossible to completely restrict thedivergence angle, and thus increase in condensed light diameter alongwith the increase in optical path length cannot be completely avoided.

On the other hand, by inserting the optical path length fixing mechanism7 as illustrated in FIG. 3, even a laser processing device using thelarge processing table 2A causing the optical path length to be largercan maintain a fixed condensed light diameter on the processing table2A, and the processing quality can be maintained.

As described above, the transmission optical system according to thethird embodiment (FIG. 3) of the present invention includes the opticalpath length fixing mechanism 7, and the optical path length fixingmechanism 7 includes the mirror group 78 constructed by a plurality ofmirrors and the moving mechanism 79 for translating the mirror group 78.The plurality of mirrors constructing the mirror group 78 are placed sothat the direction of travel of incident light to the mirror group 78and the direction of travel of output light from the mirror group 78 areopposite and in parallel to each other.

Further, the moving mechanism 79 translates the mirror group 78 withrespect to the directions of travel of the incident light and the outputlight so as to cancel out change in relative position between the laserlight L to be radiated to an object to be processed and the object to beprocessed to maintain a fixed optical path length of the laser light Lradiated to the object to be processed.

The optical path length fixing mechanism 7 is provided in this way, andhence the condensed light diameter of the laser light L radiated to anobject to be processed can be maintained independently of the relativeposition between the laser light L and the object to be processed, andthus high quality processing can be maintained.

Fourth Embodiment

Note that, in the above-mentioned third embodiment (FIG. 3), thereflective beam expander mechanism 6A including the convex mirror 61having different curvatures in two orthogonal axes and the concavemirror 62 having different curvatures in two orthogonal axes is used,but, as illustrated in FIG. 4, a reflective beam expander mechanism 6Bincluding the concave mirror 62 having different curvatures in twoorthogonal axes, the spherical convex mirror 63, a variable curvaturespherical mirror 67, and the reflection mirror 68 may also be used.

FIG. 4 is a block diagram schematically illustrating a principal part ofa laser processing device according to a fourth embodiment of thepresent invention. The same components as those described above (seeFIG. 1 to FIG. 3) are denoted by the same reference symbols as thosedescribed above, and detailed description thereof is omitted herein.

In FIG. 4, the reflective beam expander mechanism 6B according to thefourth embodiment of the present invention includes, as a transmissionoptical system, the variable curvature spherical mirror 67 that reflectsthe laser light L from the laser oscillator 1, the reflection mirror 68that reflects the laser light L reflected by the variable curvaturespherical mirror 67, and the convex mirror 61 and the concave mirror 62that reflect the laser light L reflected by the reflection mirror 68.Two orthogonal axes of each of the convex mirror 61 and the concavemirror 62 have curvatures different from each other.

The concave mirror 62 having different curvatures in two orthogonal axesreflects and introduces, into the optical path length fixing mechanism7, the laser light L reflected by the convex mirror 63 having differentcurvatures in two orthogonal axes.

Note that, the arrangement order of the variable curvature sphericalmirror 67 and the reflection mirror 68 is not limited to that in theconfiguration illustrated in FIG. 4, and the arrangement order of themirrors may be set in reverse order.

With the reflection mirror 68, it is possible to restrict the incidentangle of the laser light L with respect to the variable curvaturespherical mirror 67 so as to inhibit astigmatism that occurs in thelaser light L reflected by the variable curvature spherical mirror 67 toa range in which the processing quality is not influenced.

In the above-mentioned first to third embodiments (FIG. 1 to FIG. 3),the condensed light diameter of the laser light L at a processing pointon an object to be processed is fixed, but by providing the variablecurvature spherical mirror 67 in the reflective beam expander mechanism6B as illustrated in FIG. 4, the condensed light diameter of the laserlight can be changed.

In general, in drilling processing such as piercing processing, byappropriately changing the condensed light diameter during theprocessing, processing at higher speed can be carried out compared witha case where the condensed light diameter is fixed.

Further, in processing a corner portion or the like, heat is liable toaccumulate in the object to be processed and a cut surface may becomerough, but by changing the condensed light diameter during theprocessing to change the range of irradiation of the laser light to theobject to be processed, high quality and high precision processing canbe carried out.

As described above, the transmission optical system according to thefourth embodiment (FIG. 4) of the present invention includes thevariable curvature spherical mirror 67 and can change the condensedlight diameter of the laser light L radiated to an object to beprocessed, and hence, processing at higher speed and with higher qualitycan be realized.

Fifth Embodiment

Note that, in the above-mentioned fourth embodiment (FIG. 4), thereflective beam expander mechanism 6B including the reflection mirror 68is used, but, as illustrated in FIG. 5, a reflective beam expandermechanism 6C that does not require the reflection mirror 68 may also beused.

FIG. 5 is a block diagram schematically illustrating a principal part ofa laser processing device according to a fifth embodiment of the presentinvention. The same components as those described above (see FIG. 4) aredenoted by the same reference symbols as those described above, anddetailed description thereof is omitted herein.

In FIG. 5, the reflective beam expander mechanism 6C according to thefifth embodiment of the present invention includes, as a transmissionoptical system, the spherical convex mirror 63 that reflects the laserlight L from the laser oscillator 1, the variable curvature sphericalmirror 67 that reflects the laser light L reflected by the sphericalconvex mirror 63, and the concave mirror 62 having different curvaturesin two orthogonal axes.

The spherical convex mirror 63 and the variable curvature sphericalmirror 67 are placed so as to be substantially opposed to each other sothat the laser light L that has entered the corresponding mirror isemitted to an opposite direction.

The concave mirror 62 reflects the laser light L reflected by thevariable curvature spherical mirror 67 to introduce the laser light L tothe optical path length fixing mechanism 7 side.

The reflective beam expander mechanism 6B described above (FIG. 4)requires the reflection mirror 68 for restricting the incident anglewith respect to the variable curvature spherical mirror 67 in order toinhibit astigmatism. The reflective beam expander mechanism 6Cillustrated in FIG. 5 does not require the reflection mirror 68, becausethe spherical convex mirror 63 is placed on an incident side of thevariable curvature spherical mirror 67 and the variable curvaturespherical mirror 67 and the spherical convex mirror 63 are placed so asto be opposed to each other.

Specifically, by using the reflective beam expander mechanism 6Cillustrated in FIG. 5, the reflection mirror 68 is unnecessary and theincident angles of the laser light L with respect to the variablecurvature spherical mirror 67 and the spherical convex mirror 63,respectively, can be restricted to a range in which astigmatism does notinfluence the processing quality.

Further, simplification of the transmission optical system reduces theinfluence of thermal lenses of the optical elements, and thus, stableprocessing can be realized. Further, because the transmission opticalsystem is simplified, the optical path design flexibility can beenhanced.

As described above, the reflective beam expander mechanism 6C accordingto the fifth embodiment (FIG. 5) of the present invention includes thevariable curvature spherical mirror 67 and the spherical convex mirror63 (spherical mirror), and the variable curvature spherical mirror 67 isplaced so as to be opposed to the spherical convex mirror 63 in thereflective beam expander mechanism 6C.

This improves the processing precision as in the above description, andby placing the spherical convex mirror 63 and the variable curvaturespherical mirror 67 so as to be opposed to each other, the reflectionmirror 68 for restricting the incident angles of the laser light L withrespect to the mirrors to acute angles, respectively, becomesunnecessary. Thus, the processing can be stabilized throughsimplification of the optical path and reduction in thermal lens effect.

Sixth Embodiment

Note that, in the above-mentioned fifth embodiment (FIG. 5), thereflective beam expander mechanism 6C including the concave mirror 62having different curvatures in two orthogonal axes and the variablecurvature spherical mirror 67 is used, but, as illustrated in FIG. 6, areflective beam expander mechanism 6D including a variable curvaturemirror 64 having changeable curvatures in two orthogonal axes may alsobe used.

FIG. 6 is a block diagram schematically illustrating a principal part ofa laser processing device according to a sixth embodiment of the presentinvention. The same components as those described above (see FIG. 5) aredenoted by the same reference symbols as those described above, anddetailed description thereof is omitted herein.

In FIG. 6, the reflective beam expander mechanism 6D according to thesixth embodiment of the present invention includes, as a transmissionoptical system, the spherical convex mirror 63 that reflects the laserlight L from the laser oscillator 1 and the variable curvature mirror 64having changeable curvatures in two orthogonal axes.

The variable curvature mirror 64 having changeable curvatures in twoorthogonal axes has the function of both the concave mirror 62 havingdifferent curvatures in two orthogonal axes and the variable curvaturespherical mirror 67 described above (FIG. 5), and the variable curvaturemirror 64 reflects the laser light L reflected by the spherical convexmirror 63 to introduce the laser light L to the optical path lengthfixing mechanism 7 side.

By using the reflective beam expander mechanism 6D illustrated in FIG.6, the transmission optical system is simplified and the number of theoptical elements is reduced. Thus, the influence of thermal lenses canbe further reduced, and in addition, stable processing can be realized.Further, the transmission optical system is simplified, and hence theoptical path design flexibility can be enhanced.

As described above, the reflective beam expander mechanism 6D accordingto the sixth embodiment (FIG. 6) of the present invention includes thevariable curvature mirror 64 having changeable curvatures in twoorthogonal axes. With the variable curvature mirror 64, both the mirrorhaving different curvatures in two orthogonal axes and the variablecurvature spherical mirror described above can be collected as a singleoptical element.

Therefore, the number of the optical elements can be reduced, and thestabilization of the processing precision can be realized throughsimplification of the optical path and reduction in thermal lens effect.

Seventh Embodiment

Note that, the convex mirror 61 having different curvatures in twoorthogonal axes and the concave mirror 62 having different curvatures intwo orthogonal axes of the above-mentioned first to sixth embodiments(FIG. 1 to FIG. 6) may be provided in a mirror adjusting mechanism 90illustrated in FIG. 8.

In FIG. 8, the mirror adjusting mechanism 90 includes a mechanism thatcan move a fixed mirror in a horizontal direction and in a verticaldirection and can rotate the fixed mirror within a mirror plane about acenter of the mirror by using a horizontal direction adjustment screw91, a vertical direction adjustment screw 92, and a rotational directionadjustment screw 93.

The convex mirror 61 and the concave mirror 62 each having differentcurvatures in two orthogonal axes have lower precision curvatures aroundedges thereof due to a problem of processing precision of a sphericalsurface, and thus it is desired to radiate the laser light L to thevicinity of centers thereof. However, a pass line of the laser light Lchanges depending on thermal loads of the transmission optical systemand the oscillator and change in surrounding environments such astemperature and humidity.

Further, when an incidence plane of the laser light L deviates from anaxis along which the curvature is designed, a beam has a shape of anellipsoid of revolution, and the processing quality is lowered.

By the mirror adjusting mechanism 90 illustrated in FIG. 8, even if thepass line of the laser light L changes, the laser light L is radiated tocenters of the convex mirror 61 and the concave mirror 62 each havingdifferent curvatures in two orthogonal axes, and the laser light can betransmitted without distortion of the beam shape. Note that, in thisembodiment, the mirror adjusting mechanism 90 is a mechanism thatcarries out adjustment with the horizontal direction adjustment screw91, the vertical direction adjustment screw 92, and the rotationaldirection adjustment screw 93, but a piezoelectric element may be usedinstead of a screw.

1. A laser processing device, comprising: a laser oscillator for emitting laser light; a processing table on which an object to be processed is placed; a transmission optical system for transmitting the laser light emitted from the laser oscillator to the processing table; a processing head for condensing and radiating the laser light transmitted via the transmission optical system to the object to be processed; and moving means for changing a relative position between the object to be processed and the laser light to be radiated to the object to be processed, wherein the transmission optical system comprises a reflective beam expander mechanism for collimating and magnifying the laser light from the laser oscillator, and wherein the reflective beam expander mechanism comprises a mirror having different curvatures in two orthogonal axes.
 2. A laser processing device according to claim 1, wherein the transmission optical system comprises an optical path length fixing mechanism placed at a position capable of receiving the laser light emitted from the mirror having different curvatures in two orthogonal axes, wherein the optical path length fixing mechanism comprises a mirror group including a plurality of mirrors and a moving mechanism for translating the mirror group, wherein the plurality of mirrors of the mirror group are placed so that a direction of travel of incident light to the mirror group and a direction of travel of output light from the mirror group are opposite and in parallel to each other, and wherein the moving mechanism translates the mirror group with respect to the direction of the travel of the incident light and the direction of the travel of the output light so as to cancel out change in relative position between the object to be processed and the laser light to be radiated to the object to be processed to maintain a fixed optical path length of the laser light radiated to the object to be processed. 